Comment by crdoconnor

In my experience

* Configuration files are best made with YAML (it's the most human readable).

* APIs / other forms of serialization/deserialization over a network are best done with JSON (chop it in half and it will fail fast unlike yaml. still fairly readable tho).

* Programming languages (like ant) should not be written in either one ever (fortunately I've never heard of a YAML or JSON based language).

* XML does a bad to terrible job of all three.